I found this at http://powershell.com/cs/blogs/tips/archive/2012/02/20/make-powershell-speak.aspx. I haven't seen it on here. This could get pretty interesting.
I've added this to the end of a few scripts that I have. Users think their computers are magical.
Add-Type -AssemblyName System.Speech
$synthesizer = New-Object -TypeName System.Speech.Synthesis.SpeechSynthesizer
$synthesizer.Speak('Installation Complete. Please reboot at your earliest convenience!')